1. Field of the Invention
The invention relates to a gearshift mechanism for bicycles having a shifting aid which facilitates shifting a chain from a larger to a smaller sprocket and shifting back to the larger sprocket.
2. Description of the Related Art
German reference DE 44 45 035 C1 discloses a gearshift mechanism for a bicycle with a set of driving sprocket wheels, the larger sprocket wheel of which has shifting aids on its side facing the smaller sprocket wheel. The shifting aids, which are in the form of cone rivets, facilitate shifting from the smaller sprocket wheel to the larger sprocket wheel. These cone rivets project from the side of the larger sprocket, but are out of the running plane of the chain. If the chain is moved axially towards these aids by a shifting device, the cone rivets pick up the chain, thus facilitating shifting the chain onto the respectively larger sprocket wheel. On the other hand, although shifting the chain from the larger sprocket wheel to the smaller sprocket wheel is simpler, the cone rivets are not involved in controlled deflection of the chain during that process. Therefore, the chain can be shifted even at transfer areas of the sprocket which were not designed for that purpose.